The present invention relates to a pneumatic conveyor for powdery and granular materials, and more particularly to a constant discharge device in such a conveyor having a discharge nozzle in a pressure tank.
Pressure tanks for pneumatic conveyors generally include a fluidizing system disposed adjacent to a discharge nozzle for fluidizing a powdery or granular material in the pressure tank. Constant discharge of the material in its fluidized state from the pressure tank is controlled by a loss-in-weight feeder system in which the rate of flow of conveying air is controlled to keep constant the rate of change of the measured weight of the tank with respect to time, or by a constant flow control system in which the rate of flow of conveying air is controlled on the basis of the weight and rate of flow of the material which is being conveyed through a discharge pipe. The prior constant discharge systems are however disadvantageous in that the material being conveyed is not fluidized sufficiently stably, and hence the rate of flow of the material as fed into the discharge pipe is not kept constant, resulting in a failure to achieve precise constant flow control.